Duane Underwood has given up one earned run or fewer in seven of his last nine games. (Mike Janes/Four Seam Images)

The third inning of Saturday's game represented Clinton's best chance to produce something against Kane County starter Duane Underwood. He made sure that didn't happen.

The Cubs prospect did not allow the LumberKings' second and third hits to prevent him from shutting the door in that inning. And once that door was closed, Underwood retired the final 11 batters of his six scoreless innings, paving the way to the Cougars' 4-0 road win.

"Everything just came together," the 2012 second-round pick said. "I was able to make some pitches and get inside on the guys and keep the hitters off-balance. On the three hits, I missed with a couple pitches up. But for the most part, I was able to contain the hits to just hits and not advancing any runners and not letting any runs score."

Underwood (3-2) set a career high with six strikeouts, walking none and yielding just the three hits. Chantz Mack singled with two outs in the first before Martin Peguero started the third with a double and Luis Caballero singled.

The reason Underwood didn't sweat too much after Caballero's hit was because he had just picked off Peguero.

"We've actually worked on it a lot," the 19-year-old right-hander said. "I know I've done some side work with our shortstop and our first baseman to make sure we have those things down, so when the time is needed, I can get those outs."

The Georgia native responded to Caballero's single by fanning Aaron Barbosa and getting a flyout from Jack Reinheimer. His final three innings were perfect, just like his second.

Underwood gave credit to catcher Kyle Schwarber for helping him enter that groove.

"Once me and Schwarber got on the same page, it was pretty much like clockwork," he said. "He was calling it where I wanted to throw it. That's just the kind of relationship you want to have with your catcher. He's confident in what he's calling, and you can be confident in what you have -- you just know you're going to throw that strike there. You know you're going to throw that when you have you and your catcher on the same page."

Underwood shaved nearly a third of a run off his ERA, lowering it to 2.54. Twelve of his 13 appearances this year have been starts, and he has 40 strikeouts against 23 walks over 56 2/3 innings.

In seven of his last nine outings, Underwood has kept his opponent to one earned run or fewer. It'd be tough to argue that any of the first eight went better than Saturday, in which he did not issue a walk for the first time all year.

"My fastball has pretty much been there, but my off-speed stuff and being able to control it to both sides of the plate, that was something we've been working on," he said. "It just really came together there and it's been coming together for these last couple outings."

Relievers Jose Arias and Michael Heesch pitched the final three innings, with Arias getting a hold after posting two hitless frames. Carlos Penalver drove in the Cougars' first two runs in with a two-out single in the third.

Edwin Diaz (2-5) gave up Penalver's hit and was charged with two runs and three hits over 5 2/3 innings. The Mariners' No. 4 prospect struck out six and walked two.

Mark Emery is a contributor to MiLB.com. Follow him on Twitter @Mark_Emery. This story was not subject to the approval of the National Association of Professional Baseball Leagues or its clubs.